Although many medical conditions are satisfactorily treated by the general systemic administration of a therapeutic agent, the treatment of a many conditions require delivery of the therapeutic agent locally within a body vessel to a selected portion of internal body tissue, without delivery of the therapeutic agent to surrounding tissue or requiring systemic delivery of the therapeutic agent. A systemically administered therapeutic agent may be absorbed not only by the tissues at the target site, but by other areas of the body. As such, one drawback associated with the systemic administration of therapeutic agents is that areas of the body not needing treatment are also affected.
Medical delivery catheters provide a minimally invasive means for delivering therapeutic agents to internal body tissue. To provide site-specific localized treatment, balloon catheters may be used to deliver a therapeutic agent exclusively to the target site within a body vessel. One example of a condition that is beneficially treated by local administration of a therapeutic agent with a balloon catheter is the delivery of a therapeutic agent in combination with percutaneous transluminal coronary angioplasty (PTCA), a technique used to dilate stenotic portions of blood vessels. During PTCA, a catheter balloon is positioned at a blocked lumen or target site, the balloon is inflated causing dilation of the lumen. The balloon is deflated and the catheter is then removed from the target site and the patient's lumen thereby allowing blood to freely flow through the unrestricted lumen.
Although PTCA and related procedures aid in alleviating intraluminal constrictions, such constrictions or blockages may reoccur in many cases. The cause of these recurring obstructions, termed restenosis, may be due to the body responding to the surgical procedure. Restenosis of the artery commonly develops over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. Proliferation and migration of smooth muscle cells (SMC) from the media layer of the lumen to the intima cause an excessive production of extra cellular matrices (ECM), which is believed to be one of the leading contributors to the development of restenosis. The extensive thickening of tissues narrows the lumen of the blood vessel, constricting or blocking the blood flow through the vessel. Therapeutic agents selected to limit or prevent restenosis may be locally delivered with PTCA from a catheter and/or by placement of a stent configured to release the therapeutic agent after the PTCA procedure. Catheter balloons may be used in combination with stents, synthetic vascular grafts or drug therapies, during the PTCA procedure to reduce or eliminate the incidence of restenosis.
A number of catheter devices have been developed to administer a therapeutic agent locally to tissue while dilating a body vessel, such as during delivery of a therapeutic agent to a dilated portion of a coronary artery in a PTCA procedure. For instance, a therapeutic agent may be administered directly to the target site through small holes or apertures in the wall of a catheter balloon.
For example, U.S. Pat. No. 4,994,033 to Shockey et al. discloses a double balloon catheter for the application of medication to a blood vessel wall, for example to a stenosis. The distal portion of the catheter includes an inner balloon enclosed by a porous outer balloon. In operation, a therapeutic agent may be administered through a lumen in communication with the annular space between the inner and the outer balloon in the catheter, and is released through an array of minute holes or micropores in the outer balloon as the medication flows into the balloon through a lumen in the catheter shaft. The fluid medication is released by the action of pressurization in the lumen in communication with the outer balloon and forced out of the holes or micropores. However, at pressures of about 0.2 MPa (2 atmospheres) and above, the velocity of fluid that passes out of the holes of such a balloon often can create a forceful stream which directly impinges the arterial wall in a manner that may cause tissue damage.
U.S. Pat. No. 5,049,132 to Shaffer et al. describes a dual balloon catheter assembly having two concentric balloons in communication with separate lumens formed in the catheter shaft. A first non-perforated balloon is in communication with a first inflation lumen. A second, perforated, balloon is disposed around the first balloon and is in separate communication with a second inflation lumen. In addition, the catheter shaft may include a third separate lumen adapted to slidably house a guidewire for placement of the catheter assembly. However, the lumens of the catheter assembly are integrally formed in the catheter shaft, which may compromise tractability and pushability of the catheter system within a body vessel.
However, current fluid delivery catheters may suffer from a number of disadvantages that may limit the practical effectiveness of these devices, such as: (1) an inability to separately control the inflation of the balloon and the release of a liquid therapeutic agent, (2) increased diameter limiting the ability of the catheter to pass through a stenotic treatment site within a blood vessel (crossability), (3) undesirably compromised ability to curve while being translated within the blood vessel (tractability), (4) undesirably compromised ability to transmit a force when the balloon catheter is inserted into a blood vessel (pushability) or (5) an ability to inflate a dilation balloon on the distal portion of the catheter shaft to high pressures using a desirably flexible and low-profile catheter shaft. Kink resistance is an example of a characteristic relating to pushability. While reducing the profile (thickness) of catheter shaft may improve the crossability of the catheter, this may degrade pushability. Further, increasing rigidity of catheter shaft improves pushability and kink resistance, but tends to degrade crossability. In addition, the distal portion of the flow directed catheter must be extremely flexible so that it is capable of tracking the intricate vasculature to the site to be accessed under the influence of flow in the vessel. Consequently, conventional flow directed catheters have had distal portions formed of material which is extremely flexible, and which is also quite soft. Typically, the softer the material, the lower the burst pressure. Thus, some conventional fluid delivery catheters are formed with distal shaft portions with undesirably low burst pressure. This can cause the catheter to burst when injectant is introduced through the catheter. In other words, all the above-mentioned characteristics are closely related to each other, and it is not easy to improve all the characteristics at the same time while providing simultaneous independent control of the rate of drug delivery and inflation of a dual balloon catheter for delivering a therapeutic agent. There remains a need for a therapeutic balloon catheter for expanding a body vessel and administering medication to the body vessel wall while possessing improved or suitable catheter shaft burst pressure, crossability, pushability and tractability for an intended medical application.